The invention relates to a disengageable cylinder for an automobile lock mechanism.
The addition of a disengageable mechanism to a cylinder intended for an automobile lock makes it possible to prevent this cylinder from being forced. Specifically, if an improper key, or any other flat tool of suitable shape, is inserted into the rotor, and if an attempt is then made to rotate the rotor, the disengagement mechanism enables the rotor and an intermediate sleeve to pivot freely inside the stator without considerable stresses being exerted on the tumblers.
The fact is that, in the presence of excessive stresses, the tumblers are liable to be damaged or be retracted by force, thus allowing the cylinder to be unlocked without the appropriate key.
The invention is concerned more precisely with a disengageable cylinder, in particular for a motor vehicle lock mechanism, comprising a fixed stator, a tubular intermediate sleeve which is mounted in rotation about its axis in the stator and which is fixed axially with respect to the stator, a rotor which is mounted in rotation in the sleeve, which is fixed axially in the sleeve and which comprises tumblers which can move radially under the action of a key intended to be inserted axially into the rotor. Tumblers are fully retracted inside the rotor when the key is appropriate, so as to allow a free rotation of the rotor with respect to the sleeve and the stator and thus allow a lock operating lever, called a cam actuator, to be rotated, this lever being coupled to the rotor via a driver. The rotor and the intermediate sleeve are blocked against rotation with respect to one another by the tumblers when the key is not appropriate. The cylinder also comprises an indexer which can move axially between a rest position and a disengagement position, under the effect of a rotation of the sleeve with respect to the stator subsequent to the rotor being rotated by means of an inappropriate key, so as to move the driver axially toward a disengaged position.
Such a disengageable cylinder is described in patent document FR 2 748 513.
In this known cylinder, the indexer and the driver are in a configuration with a substantially end-to-end arrangement. These two parts are substantially arranged as a continuation of one another.
The indexer is coupled in rotation with the intermediate sleeve and is guided in translation therein. The driver for its part is guided in rotation on the rotor.
The indexer comprises a main ring and guide tabs which extend axially from the ring and which are intended to be accommodated in corresponding axial notches of the intermediate sleeve. It also comprises two lugs which extend axially in the opposite direction in the continuation of two diametrically opposed guide tabs.
This cylinder arrangement poses the following technical problems.
Due to its configuration with an end-to-end arrangement, the length of such a cylinder is relatively large.
Moreover, the indexer is a relatively fragile part due to its construction.